Flame-retardant molding compositions

ABSTRACT

A flame-retardant molding composition that includes an epoxy resin, melamine cyanurate, and one or more hydrated metal salts capable of liberating water when heated. The hydrated metal salt may include one or more compounds selected from metal borate salts, Group IIB oxides, and polyhydroxides of one or more elements selected from Group IIA elements and Group IIIB elements. The molding composition may be used to coat an electrical or electronic device by heating the molding composition to a temperature sufficient to cure the molding composition and form a polymer on the surface of the device. Electrical and electronic devices formed by the method are also disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to molding compounds for electrical andelectronic devices, particularly epoxy-based compounds exhibiting flameresistance, moisture resistance, and low warpage and shrinkage.

2. Brief Description of Related Technology

Epoxy resins are widely used in molding compounds for coating electricaland electronic devices. Such epoxy molding compounds used forencapsulation are generally prepared from a blend of an epoxy resin andphenol hardener, along with other ingredients including fillers,catalysts, flame-retardant materials, processing aids, and colorants.Epoxy resins in such molding compounds are traditionally diepoxideswhich include two epoxy groups per molecule, which are reacted with aco-reactant (cross-linking agent or hardener) consisting of aciddianhydride, diamine, or diphenol oligomers. Diphenol oligomers, such asthose derived from novolac phenols, cresol phenols and bisphenol A, areparticularly preferred in the art as hardeners due to their highreliability.

Flame-retardants in epoxy compositions are typically provided for safetypurposes. A common flame-retardant system is a combination ofbromine-containing flame-retardants and antimony oxide flame-retardantsynergists. However, these compounds are pollutants of the environment.Some bromine-containing flame-retardants (especially brominated diphenylethers) are toxic and possibly carcinogenic. Antimony trioxide isclassified by the International Agency for Research on Cancer as a Class2B carcinogen (i.e., antimony trioxide is a suspect carcinogen basedmainly on animal studies). In addition, this compound is often used at arelatively high level (2-4%) and is also slightly water-soluble, leadingto further environmental concerns. This concern is highlighted by thefact that integrated circuit manufacturers currently discard up to onehalf of the total amount of molding compositions used.

Phosphorus-containing compounds have been proposed as flame-retardants.For example, U.S. Pat. No. 5,739,187 to Asano et al. discloses epoxyresin compositions as semiconductor encapsulants, which include aphosphorus-containing flame-retardant to eliminate the use of antimonytrioxide and brominated compounds. However, molding compositionscontaining conventional phosphorus compounds generally possessundesirable properties such as high moisture absorption, which can causestress and cracking of the encapsulant at elevated temperatures.

Melamine cyanurate is commonly sold as a flame-retardant compound.Although effective as a flame-retardant, high levels of this materialoftentimes severely reduce the flowability of molding compounds. As aresult, it has generally been considered impractical to incorporatemelamine cyanurate into molding compounds at appropriate levels toachieve both adequate flame retardancy and flowability.

Unfortunately, reducing the amount of the flame-retardant to address theflowability issues compromises flame retardance, with the resultingmolding compounds failing to meet the flame retardance standard, UL-94V-O rating.

It would be desirable to provide new flame-retardant moldingcompositions that overcome these, while providing commerciallyacceptable physical properties. Moreover, it would be desirable toprovide molding compositions with excellent stress characteristics suchas low warpage and shrinkage with improved flowability upon curing.

SUMMARY OF THE INVENTION

The present invention provides a flame-retardant molding compositionsubstantially free of elemental halogen, phosphorus, and antimony, thatincludes an epoxy resin, melamine cyanurate, and one or more hydratedmetal salts capable of liberating water when heated. In an embodiment ofthe invention, the hydrated metal salt may include one or more compoundsselected from metal borate salts, Group IIB oxides, and polyhydroxidesof one or more elements selected from Group IIA elements and Group IIIBelements.

The present invention is also directed to a method of coating anelectrical or electronic device. The inventive method includes heatingthe above-described molding composition to a temperature sufficient tocure the molding composition and form a polymer on the surface of thedevice. The present invention is further directed to electrical andelectronic devices formed by the present method.

Other features and advantages of the invention will be apparent from thedescription of the preferred embodiments thereof and from the claims.

DETAILED DESCRIPTION OF THE INVENTION

Other than in the operating examples, or where otherwise indicated, allnumbers or expressions referring to quantities of ingredients, reactionconditions, etc., used in the specification and claims are to beunderstood as modified in all instances by the term “about.” Variousnumerical ranges are disclosed in this patent application. Because theseranges are continuous, they include every value between the minimum andmaximum values. Unless expressly indicated otherwise, the variousnumerical ranges specified in this application are approximations.

As used herein, the term “substantially free” is meant to indicate thata material is present as an incidental impurity. In other words, thematerial is not intentionally added to an indicated composition, but maybe present at minor or inconsequential levels because it was carriedover as an impurity as part of an intended composition component.

As used herein the term “cured” is meant to indicate a three-dimensionalcrosslink network formed by covalent bond formation, e.g., between thefunctional groups of the hardener and the epoxy groups of the resin. Thetemperature at which the composition of the present invention cures isvariable, and depends in part on the conditions and the type and amountof catalyst, if any is used.

As used herein the term “hydrated metal salts” is meant to indicatemetal salts that contain water in the form of water of crystallization,i.e. water present in metal salt crystals in definite proportions, suchas water molecules that occupy lattice positions in the metal saltcrystals. Hydrated metal salts useful in the present invention liberateat least a portion of the water they contain when heated.

The present invention is directed to a flame-retardant moldingcomposition that is substantially free of elemental halogen, phosphorus,and antimony. The inventive molding composition includes an epoxy resin,melamine cyanurate, and one or more hydrated metal salts capable ofliberating water when heated.

There is no restriction on the type of epoxy resin that can be used inthe molding compositions. Desirably, the epoxy resin contains two ormore reactive oxirane groups. For example, the epoxy resin may beselected from, but not limited to, bisphenol A type epoxy resins;novolac type epoxy resins, such as epoxy cresol novolac resin andphenolic novolac epoxy resin; alicyclic epoxy resins; glycidyl typeepoxy resins; biphenyl epoxy resins; naphthalene ring-containing epoxyresins; cyclopentadiene-containing epoxy resins; polyfunctional epoxyresins; hydroquinone epoxy resins; and stilbene epoxy resins. Themolding compositions can include more than one epoxy resin; for example,a combination of epoxy cresol novolac resin and biphenyl epoxy resin.

As noted, bisphenol and biphenyl epoxy resins, which are traditionallyreferenced as di-epoxies, and epoxy cresol novolac resins, which aretraditionally referenced as multifunctional epoxies, are useful in thepresent invention. Such epoxies have a degree of branching of two, inthat two phenolic groups having pendant epoxies are linked through thesame carbon atom. For example, diglycidyl ether of bisphenol A isdifunctional, including two phenolic groups with pendant epoxiesextending from a central carbon atom. It therefore has a degree ofbranching of two. Epoxy cresol novolac resins are oftentimes referencedas “multifunctional,” in that they are polymeric compounds with aplurality of pendant epoxy moieties which may extend from the polymericchain. For example, epoxy cresol novolac resins include the followingstructure:

In the instance where n=0, the functionality of this structure would be2. If n=1, the functionality, is 3; if n=4, the functionality is 6; etc.As such, this compound is traditionally referred to as a multifunctionalepoxy resin. However, since only two phenolic groups extend from thesame carbon or small cluster of carbons, the degree of branching of thistype of resin would be equal to two.

In a particularly desirable embodiment, the epoxy resin is amultifunctional epoxy resin having a degree of branching within theresin backbone of at least three. Thus, particularly desirablemultifunctional epoxy resins are those derived from phenol, and whichinclude at least three phenolic groups branching directly from the samecentral carbon atom or central cluster of carbons, with a pendantoxirane group linked to each of the at least three phenolic groups.

Non-limiting examples of useful multifunctional epoxy resins having adegree of branching of at least three include:

triphenylol methane triglycidyl ether (having a degree of branching ofthree, represented by three terminal glycidyl ether moieties branchingfrom a central carbon atom); and

tetra glycidyl ether of tetra phenol ethane (having a degree ofbranching of four, represented by four terminal glycidyl ether moietiesbranching from a central two carbon cluster ethyl moiety).

Particularly desirable are epoxy resins derived from tris-phenolmethane,such as triphenylol methane triglycidyl ether.

The multifunctional resin having a degree of branching of at least threemay be used alone, or in combination with conventional resins such asthose described above.

The epoxy resin typically has a theoretical epoxy equivalent weight ofabout 150 to 250.

The present molding composition contains the epoxy resin at a level ofat least 1 percent, in some case at least 4 percent, in other cases atleast 5 percent, and in some situations at least 5.5 percent by weightof the molding composition. Also, the epoxy resin is present in anamount of up to 12 percent, in some cases up to 11 percent, in othercases up to 9 percent and in some situations up to 8.5 percent by weightof the molding composition. The molding composition may contain theepoxy resin in any range of values inclusive of those stated above.

A curing agent (hardener) may be included in the present moldingcomposition. The hardener promotes crosslinking of the moldingcomposition to form a polymer composition upon heating of thecomposition to a temperature of at least 135° C. Some suitable curingagents that can be included in the molding compositions of the presentinvention are phenol novolac type hardener, cresol novolac typehardener, dicyclopentadiene phenol type hardener, limonene typehardener, and anhydrides. Flexible hardeners having a hydroxylequivalent weight greater than about 150 are often desirable, such asxylock novolac type hardener. Non-limiting examples of flexiblehardeners include bisphenol M, commercially available from BordenChemical, and DEH 85, commercially available from Dow Chemical. Similarto the epoxy resin component, more than one type of curing agent can beincluded in the molding compositions. The hardener typically has anepoxy equivalent weight of about 100 to 150.

As with the epoxy resin component, multifunctional hardeners having adegree of branching of at least three are particularly desirable in oneembodiment of the present invention. Particularly desirable are thosederived from tris-phenol and which contain at least three functionalgroups that are reactive with epoxide groups.

The present molding composition contains the hardener at a level of atleast 1 percent, in some case at least 1.5 percent, in other cases atleast 2 percent, and in some situations at least 2.5 percent by weightof the molding composition. Also, the hardener is present in an amountof up to 10 percent, in some cases up to 9 percent, in other cases up to8 percent and in some situations up to 6 percent by weight of themolding composition. The molding composition may contain the hardener inany range of values inclusive of those stated above.

The composition may, optionally, also include a catalyst for promotingreaction of the epoxy resin and the hardener. Traditionally, such epoxycompositions incorporate catalysts such as tertiary amines, substitutedphosphines, salts of quaternary organophosphonium compounds, imidazoles,and the like, with compounds such as 1,8-diazabicyclo[5.4.0]undec-7-ene(“DBU”), dicyandiamide (“DICY”) and triphenylphosphine (“TPP”) beingparticularly well known for use as catalysts. Salts of quaternaryorganophosphonium compounds which may be used include, but are notlimited to, organophosphonium functional acetic acid ester compounds,such as ethyltriphenylphosphonium acid acetate complex (“EtTPPOAc”),commercially available from Rohm and Haas.

In addition, the composition of the present invention further includescomponents specifically designated for imparting flame retardancy to thecomposition. One component included in the composition to impart flameretardancy is melamine cyanurate. Additionally, the present moldingcomposition includes hydrated metal salts that liberate water whenheated. In an embodiment of the present invention, water is liberatedfrom the hydrated metal salts when they are heated above 100° C., insome cases when heated above 125° C., and in other cases when heatedabove 150° C. While not being limited to a single theory, it is believedthat the liberation of water from the hydrated metal salts helps toprovide flame retardancy properties to the present molding composition.

Any suitable hydrated metal salts may be used in the present invention.In an embodiment of the present invention, the suitable hydrated metalsalts include, but are not limited to, metal borate salts, Group IIBoxides, and polyhydroxides of one or more elements selected from GroupIIA elements and Group IIIB elements.

As a non-limiting example, the metal borate salts may include zincborate. As a further non-limiting example, the Group IIB oxides mayinclude zinc oxide. In an additional non-limiting example, thepolyhydroxides may include one or both of aluminum trihydrate (Al(OH)₃)and magnesium hydroxide (Mg(OH)₂).

The present molding composition contains melamine cyanurate at a levelof at least 0.1 percent, in some case at least 0.25 percent, in othercases at least 0.5 percent, and in some situations at least 1 percent byweight of the molding composition. The melamine cyanurate is present ata level sufficient to impart the desired fire retardancy properties.Also, melamine cyanurate is present in an amount of up to 4 percent, insome cases up to 3.5 percent, in other cases up to 3 percent, and insome situations up to 2.5 percent by weight of the molding composition.If the amount of melamine cyanurate is too high, the viscosity of themolding composition may be too high and the molding composition maybecome difficult to handle. The molding composition may contain melaminecyanurate in any range of values inclusive of those stated above.

The present molding composition contains the metal borate salt at alevel of at least 0.1 percent, in some case at least 0.2 percent, inother cases at least 0.3 percent, in some situations at least 0.4percent, and in other situations at least 0.5 percent by weight of themolding composition. The metal borate salt is present at a levelsufficient to impart the desired fire retardancy properties incombination with the melamine cyanurate. The metal borate salt ispresent in an amount of up to 2 percent, in some cases up to 1.75percent, in other cases up to 1.5 percent, and in some situations up to1 percent by weight of the molding composition. If the amount of themetal borate salt is too high, the viscosity of the molding compositionmay be too high and the molding composition may become difficult tohandle. The molding composition may contain the metal borate salt in anyrange of values inclusive of those stated above.

The present molding composition may optionally contain a polyhydroxideof one or more elements selected from Group IIA elements and Group IIIBelements. When the polyhydroxide is present, it may be present at alevel of at least 0.1 percent, in some case at least 0.15 percent, inother cases at least 0.2 percent, and in some situations at least 0.25percent by weight of the molding composition. The polyhydroxide ispresent at a level sufficient to impart the desired fire retardancyproperties in combination with the additional flame-retardantcomponents. The polyhydroxide is present in an amount of up to 1percent, in some cases up to 0.85 percent, in other cases up to 0.75percent, and in some situations up to 0.5 percent by weight of themolding composition. If the amount of the polyhydroxide is too high, theviscosity of the molding composition may be too high and the moldingcomposition may become difficult to handle. The molding composition maycontain the polyhydroxide in any range of values inclusive of thosestated above.

The present molding composition may optionally contain a Group IIB metaloxide. When the metal oxide is present, it may be present at a level ofat least 0.1 percent, in some case at least 0.15 percent, in other casesat least 0.2 percent, and in some situations at least 0.25 percent byweight of the molding composition. The metal oxide is present at a levelsufficient to impart the desired fire retardancy properties incombination with the additional flame-retardant components. The metaloxide is present in an amount of up to 1 percent, in some cases up to0.85 percent, in other cases up to 0.75 percent, and in some situationsup to 0.5 percent by weight of the molding composition. If the amount ofthe metal oxide is too high, the viscosity of the molding compositionmay be too high and the molding composition may become difficult tohandle. The molding composition may contain the metal oxide in any rangeof values inclusive of those stated above.

In an embodiment of the present invention, the molding compositioncontains an epoxy resin, melamine cyanurate, zinc borate, and a compoundselected from zinc oxide, aluminum trihydrate, and/or magnesiumhydroxide. In a non-limiting example of this embodiment, the melaminecyanurate is present in an amount from about 0.1 to about 3.5 percent byweight of the molding composition; zinc borate is present in an amountfrom about 0.1 to about 2 percent by weight of the molding composition;zinc oxide is present in an amount from about 0 to about 1 percent byweight of the molding composition; and the metal polyhydroxide ispresent in an amount from about 0 to about 1 percent by weight of themolding composition.

The present molding composition may include other suitableflame-retardants known in the art in addition to those set forth above.Non-limiting examples of suitable flame-retardants include, but are notlimited to, transition metal oxides such as tungsten trioxide,molybdenum trioxide, zinc molybdate, calcium molybdate, and mixturesthereof. The other flame-retardant may be present in the composition ofthe present invention in an amount of up to about 3 percent by weightbased on the total weight of the composition, optionally from about 0.4percent by weight to about 2.8 percent by weight.

In an embodiment of the present invention, the molding compositionincludes melamine cyanurate in combination with zinc oxide andoptionally aluminum trihydrate and/or magnesium hydroxide. In thisembodiment, the amount of melamine cyanurate can be decreased below thelevel typically required to impart flame retardance to a moldingcomposition, which may also serve to limit any deleterious effect inother properties which may be caused by increased levels of melaminecyanurate, such as flowability, as well as environmental concerns.

The compositions of the present invention can include other optionaladditives well known to those of skill on the art. For example, fillerssuch as silica, alumina, aluminosilicate, silicon nitride, clay, talc,mica, kaolin, calcium carbonate, wollastonite, montmorillonite,smectite, and combinations thereof are commonly present in thecomposition in amounts of about 20 to 90 percent by weight, oftendesirably from about 50 to 90 percent by weight, and more desirably fromabout 60 to 90 percent by weight based on the total weight of thecomposition.

A colorant, such as carbon black colorant, may be included in thecomposition of the present invention in amounts of about 0 to about 2percent by weight, more often, from about 0.1 to about 1 percent byweight, when present.

A mold release agent, such as carnauba wax, paraffin wax, polyethylenewax, ester waxes (such as EWAX commercially available from HoechstChemical), acid waxes (such as SWAX commercially available from HoechstChemical), glycerol monostearate, and metallic stearates, may beincluded in the composition of the present invention in amounts of fromabout 0 to about 2 percent by weight, more often, from about 0.2 toabout 1 percent by weight, when present.

A coupling agent, such as a silane type coupling agent, may be includedin the composition of the present invention in amounts of from about 0to about 2 percent by weight, more often from about 0.3 to about 1percent by weight, when present.

Ion scavengers, such as magnesium aluminum carbonate hydrate, which canbe obtained commercially from Kyowa Chemical Industry Co. under thetrade name “DHT-4A,” are suitable for use in the composition of thepresent invention and may be present in amounts of from about 0 to about2 percent by weight, more often from about 0.5 to about 2 percent byweight, when present.

Examples of other additives may include stress relievers, such aspolyphenyleneoxide; elastomers, such as powdered silicone; and adhesionpromoters, such as azine adhesion promoters, which may be present inamounts of from about 0 to about 3 percent by weight, when present.

Auxiliary catalysts, such as 1,8-diazabicyclo[5.4.0]undecene-7 (DBU),triphenylphosphine (TPP), dicyandiamide (DICY) and 2-methylimidazole,are suitable for use in the composition of the present invention and maybe present in amounts of from about 0 to about 10 percent by weight,more often from about 0.5 to about 2 percent by weight, when present.

In a particular embodiment of the present invention, the moldingcomposition includes about 4 wt. % to about 12 wt. % of an epoxy resin,about 0.1 wt. % to about 3.5 wt. % of melamine cyanurate, about 0.1 wt.% to about 2 wt. % of zinc borate, about 0.01 wt. % to about 1 wt. % ofa compound selected from one or more of zinc oxide and a metalpolyhydroxide comprising one or both of aluminum trihydrate andmagnesium hydroxide, about 0.001 wt. % to about 10 wt. % of a phenolicnovolac hardener, 0 wt. % to about 90 wt. % of one or more solvents, andabout 0.1 wt. % to about 10 wt. % each of one or more other additives.The other additives may include, but are not limited to, colorants, moldrelease agents, coupling agents, catalysts, ion scavengers, metaloxides, metal hydroxides, pigments, adhesion promoters, tougheningagents, UV absorbers, and antioxidants.

The molding compositions can be prepared by any conventional method. Forexample, as is known in the art, all of the compounds may be combinedand finely ground and dry blended, or the components can be mixed in astep-wise fashion to enhance homogeneous mixing. The mixture can then betreated on a hot differential roll mill, such as with a large two-rollmill (one roll heated to about 90° C., and the other cooled with tapwater), to produce uniform sheets, which are then ground to a powderafter cooling. Alternatively, the mixture can be extruded through a twinscrew extruder, as known in the art.

The present invention is also directed to a method of coating anelectrical or electronic device by heating the above-described moldingcomposition to a temperature sufficient to cure the molding compositionand form a polymer on the surface of the device. The moldingcompositions can be molded into various articles by any conventionalmethod, e.g., by using a molding apparatus, such as a transfer pressequipped with a multi-cavity mold for coating electronic devices.Suitable molding conditions include a temperature of about 150° C. toabout 200° C., in some cases about 165° C. to about 195° C., and inother cases about 175° C. to about 195° C. and a pressure of about 400psi to about 1,500 psi.

The preferred molding compositions cure in about 0.5 minute to about 3minutes, more preferably, about 1 minute to about 2 minutes. Todetermine the time for curing (i.e., minimum time needed for forming agood cull cure), the molding composition is placed in the mold press at190° C. and is inspected after a pre-set period of time (e.g., 3minutes). If a good cure (i.e., strong and not brittle) is formed, theexperiment is repeated with a shorter period of press time until theminimum time period is determined.

The molding compositions of the present invention typically demonstratea flammability rating of UL 94V-1, more preferably, a flammabilityrating of UL 94V-0. The UL 94 ratings are generally acceptedflammability performance standards for materials. They are intended toprovide an indication of a material's ability to extinguish a flame,once ignited. Several ratings can be applied based on the rate ofburning, time to extinguish, ability to resist dripping, and whether ornot drips are burning. The ratings are determined by measuring the totalburn time of a ⅛″ bar according to the UL 94 flammability test. A 94V-0indicates that burning stops within 10 seconds on a vertical specimenwith no drips allowed. A 94V-1 rating requires that burning stops within30 seconds on a vertical specimen with no drips allowed.

As noted above, in a particular embodiment of the invention, the epoxyresin is a multifunctional epoxy resin having a degree of branchingwithin the resin backbone of at least three, and the crosslinking agentis a multifunctional hardener derived from phenol and having a degree ofbranching of at least three. Particularly desirable epoxy resins aretris-phenolmethane derived resins, such as triphenolyl methanetriglycidyl ether, and particularly desirable hardeners aretris-phenolmethane derivatives. Examples of useful resins include1-trishydroxyphenylmethane glycidyl ether, such as SUMIEPOXY TMH574,commercially available from Sumitomo Corp., and EPPN 501H, commerciallyavailable from Nippon Kayaku. An example of a useful hardener is MEH7500, commercially available from Meiwa Kasei K.K.

A particular advantage of the inventive flame retardant moldingcomposition is that commercially desirable flame retardant propertiescan be achieved with little or no adverse impact on flow properties. Theinventive combination allows for significantly less melamine cyanurateto be used, which enables excellent flowability of the moldingcomposition, while the flame retardant properties are improved. As anon-limiting example, when the weight ratio of melamine cyanurate tohydrated metal salts is from 2:1 to 4:1, and in some cases 3:1,significantly lower levels of melamine cyanurate are required and themolding composition exhibits excellent flow and flame retardantproperties. As an non-limiting extension of this embodiment, thesynergistic properties of the inventive combination are found when thehydrated metal salts are selected from zinc oxide, zinc borate, Mg(OH)₂and AL(OH)₃.

As noted above, the compositions of the present invention areparticularly useful as molding compounds for electrical or electronicdevices. In a further embodiment, the present invention provides amethod for coating an electrical or electronic device. Non-limitingexamples of such electrical or electronic devices includesemiconductors, transistors, diodes, and integrated circuits. The methodinvolves providing a molding composition as discussed above, andcontacting a surface of an electronic device with the moldingcomposition, such as by coating the composition thereon. The deviceincluding the molding composition thereon is then heated to atemperature sufficient to cure the molding composition and form apolymer on the surface of the device. Desirably, the temperature towhich the molding composition is heated is typically at least 135° C.,often about 165° C. to 195° C.

The invention will now be described by the following examples. Theexamples are intended to be illustrative only and are not intended tolimit the scope of the invention.

EXAMPLES

The following examples of molding compositions were prepared by dryblending all of the components simultaneously and testing thecompositions.

Example 1

Seven molding compositions represented as Samples 1-7 were preparedaccording to the formulations as indicated in Table 1 below. Eachmolding composition contained an epoxy cresol novolac resin with astandard phenol novolac flexible hardener. With the exception ofComparative Sample 1, each composition contained melamine cyanurate,zinc borate, zinc oxide and, optionally, magnesium hydroxide as aflame-retardant formulation. The weight % (wt. %) indicated below werecalculated based on the total weight of the compositions. TABLE 1 SAMPLENO. 1 (com- para- COMPONENTS tive) 2 3 4 5 6 7 Silica Filler 79.85 78.8579.05 79.05 79.35 79.45 79.55 (wt. %) Epoxy Cresol Novolac 7.28 7.287.28 7.28 7.28 7.28 7.28 Resin (wt. %) Phenol Novolac 6.59 6.59 6.596.59 6.59 6.59 6.59 Hardener (wt. %) Carbon Black Colorant 0.30 0.300.30 0.30 0.30 0.30 0.30 (wt. %) Polyphenyleneoxide 0.8 0.8 0.8 0.8 0.80.8 0.8 Stress Reliever (wt. %) Ion Scavenger (wt. %) 0.3 0.3 0.3 0.30.3 0.3 0.3 Amine Catalyst 0.18 0.18 0.18 0.18 0.18 0.18 0.18 (wt. %)Melamine Cyanurate 3.0 3.0 2.8 3.0 3.0 2.9 2.8 (wt. %) Zinc Oxide (wt.%) 0.40 0.40 0.40 0.40 0.40 0.40 0.40 Zinc Borate (wt. %) — 1.0 0.5 0.50.5 0.5 0.5 Mg(OH)₂ (wt. %) — — 0.5 0.3 — — — Carnauba Wax (wt. %) 0.570.57 0.57 0.57 0.57 0.57 0.57 Silane Couple Agents 0.73 0.73 0.73 0.730.73 0.73 0.73 (wt. %)

Each of the molding compositions of Samples 1-7 were cured and testedfor flammability, gel time, spiral flow, total burn time and UL 94rating, with the results shown in Table 2. The flammability propertiesof the cured compositions were determined by the total burn time of five⅛″ molded bar according to the UL 94 test. Gel time was determinedthrough a standard testing procedure in which the compound is placed ona thermostatically-controlled hot plate, which is controlled at aspecified temperature. The compound is stroked with a spatula in aback-and-forth motion until it becomes stiff, with the time to stiffnessrepresenting the gel time.

Spiral flow, using ASTM D-3123, was determined by flowing a sample ofthe composition through a semicircular spiral mold in a transfer moldingpress at 175° C. until the flow ceased. When the mold cycle is complete,the mold is opened and the point of farthest continuous flow isrecorded. TABLE 2 SAMPLE NO. 1 (com- TEST para- PROCEDURE tive) 2 3 4 56 7 Flammability Test (UL 94) Total Burn Time Total 15.5 15 6.5 7.5 11.515.5 (sec) Burn UL 94 Rating HB¹ V-0² V-0² V-0² V-0² V-0² V-0² Gel Time(sec) 19 19 18.5 18.5 18 18.5 18.5 Spiral Flow (inches) 39 39 39 38 4040 41¹Horizontal Burning Test-slow burning on a horizontal specimen burningrate <76 mm/min for thickness <3 mm.²Burning stops within 10 seconds on a vertical specimen; no dripsallowed

The results of Table 2 demonstrate that molding compositions preparedwith a melamine cyanurate, zinc borate, zinc oxide and, optionally,magnesium hydroxide exhibit improved flame retardancy. In particular, acomparison of Sample 1 (which represents a comparative compositionprepared with only melamine cyanurate and zinc oxide) with Samples 2-7(which represent inventive compositions prepared with melaminecyanurate, zinc borate, zinc oxide and, optionally, magnesium hydroxide)shows that Samples 2-7 have improved flammability ratings compared withSample 1, which failed to achieve a UL94 V-O rating.

Example 2

Six molding compositions represented as Samples 8-13 were preparedaccording to the formulations as indicated in Table 3 below. Eachmolding composition contained a standard epoxy cresol novolac resin anda standard phenol novolac hardener, along with flame-retardants melaminecyanurate, zinc borate and, optionally, zinc oxide and/or magnesiumhydroxide. The weight % (wt. %) indicated below were calculated based onthe total weight of the compositions. TABLE 3 SAMPLE NO. 8 (com- para-COMPONENTS tive) 9 10 11 12 13 Silica Filler (wt. %) 80.05 79.95 79.8579.65 79.95 80.20 Epoxy Cresol Novolac 7.66 7.66 7.66 7.66 7.66 7.66Resin (wt. %) Phenol Novolac 5.11 5.11 5.11 5.11 5.11 5.11 Hardener (wt.%) Carbon Black Colorant 0.30 0.30 0.30 0.30 0.30 0.30 (wt. %) IonScavenger (wt. %) 0.8 0.8 0.8 0.8 0.8 0.8 Polyphenyleneoxide 1.1 1.1 1.11.1 1.1 1.1 Stress Reliever (wt. %) EtTPPOAc Catalyst 0.25 0.25 0.250.25 0.25 0.25 (wt. %) Melamine Cyanurate 3.0 3.0 3.0 3.0 3.0 3.0 (wt.%) Zinc Oxide (wt. %) — 0.1 0.2 0.4 0.1 0.1 Zinc Borate (wt. %) 0.250.25 0.25 0.25 0.25 0.25 Mg(OH)₂ (wt. %) 0.25 0.25 0.25 0.25 0.25 —Waxes (wt. %) 0.5 0.5 0.5 0.5 0.5 0.5 Silane Couple Agents 0.73 0.730.73 0.73 0.73 0.73 (wt. %)

Each of the molding compositions of Samples 8-13 were cured and testedfor flammability, gel time, and spiral flow in a similar manner as inExample 1, with the results shown in Table 4. TABLE 4 SAMPLE NO. 8 (com-para- TEST PROCEDURE tive) 9 10 11 12 13 Flammability Test (UL 94) TotalBurn Time (sec) 44.5 17.5 13.5 12.5 18 30 UL 94 Rating V-0¹ V-0¹ V-0¹V-0¹ V-0¹ V-0¹ Gel Time (sec) 25 25 26 26 25 25 Spiral Flow (inches) 4744 41 40 47 46¹Horizontal Burning Test - burning stops within 10 seconds on a verticalspecimen; no drips allowed.

The results of Table 4 demonstrate that molding compositions preparedwith melamine cyanurate, zinc borate, zinc oxide and, optionallymagnesium hydroxide as a flame-retardant formulation exhibit improvedflame retardancy.

The present invention has been described with reference to specificdetails of particular embodiments thereof. It is not intended that suchdetails be regarded as limitations upon the scope of the inventionexcept insofar as and to the extent that they are included in theaccompanying claims.

1-7. (canceled)
 8. A flame-retardant molding composition substantiallyfree of elemental halogen, phosphorus, and antimony, comprising: anepoxy resin; about 0.1 to about 4 wt. % based on the weight of themolding composition of melamine cyanurate; about 0.1 to about 2 wt. % ofone or more metal borate salts; and about 0.1 to about 1 wt. % of acompound selected from the group consisting of polyhydroxides of one ormore elements selected from Group IIA elements and Group IIIB elements,one or more Group IIB oxides and mixtures thereof, wherein the Group IIBoxides are present in an amount from about 0.01 to about 1 percent byweight of the molding composition.
 9. The molding composition of claim8, wherein the metal borate salt comprises zinc borate.
 10. The moldingcomposition of claim 8, wherein the polyhydroxide is a metalpolyhydroxide comprising one or more of aluminum trihydrate, magnesiumhydroxide, or calcium hydroxide, and the Group IIB oxides comprise zincoxide.
 11. The molding composition of claim 8, wherein the melaminecyanurate is present in an amount of from about 0.1 to about 3.5 percentby weight of the molding composition; the metal borate salt is presentin an amount from about 0.2 to about 1.75 percent by weight of themolding composition; the polyhydroxide is present in an amount fromabout 0.15 to about 0.85 percent by weight of the molding composition;and the Group IIB oxides are present in an amount from about 0.1 toabout 0.85 percent by weight of the molding composition.
 12. The moldingcomposition of claim 8, wherein the metal borate salt comprises zincborate, the polyhydroxide comprises one or both of aluminum trihydrateor magnesium hydroxide and the Group IIB oxides comprise zinc oxide. 13.The molding composition of claim 8, further comprising a phenolicnovolac hardener.
 14. The molding composition of claim 13, wherein theamount of the phenolic novolac hardener ranges from about 1.5 wt. % toabout 10 wt. % based on the total weight of the molding composition. 15.The molding composition of claim 8, wherein the molding compositioncomprises an epoxy cresol novolac resin.
 16. The molding composition ofclaim 8, wherein the molding composition further comprises a biphenylepoxy resin.
 17. The molding composition of claim 8, wherein the amountof the epoxy resin ranges from about 4 wt. % to about 12 wt. % based onthe total weight of the molding composition.
 18. The molding compositionof claim 17, wherein the amount of the epoxy resin ranges from about 5.5wt. % to about 8.5 wt. % based on the total weight of the moldingcomposition.
 19. A flame-retardant molding composition substantiallyfree of elemental halogen, phosphorous, and antimony, comprising anepoxy resin, from about 0.1 to about 4 percent by weight of the moldingcomposition of melamine cyanurate, from about 0.1 to about 2 percent byweight of zinc borate, and a compound selected from about 0 to about 1percent by weight of zinc oxide or from about 0 to about 1 percent byweight of a metal polyhydroxide comprising one or both of aluminumtrihydrate and magnesium hydroxide.
 20. The molding composition of claim19, wherein the melamine cyanurate is present in an amount from about0.1 to about 3.5 percent by weight of the molding composition; zincborate is present in an amount from about 0.2 to about 1.75 percent byweight of the molding composition; zinc oxide is present in an amountfrom about 0.1 to about 1 percent by weight of the molding composition;and the metal polyhydroxide is present in an amount from about 0.1 toabout 1 percent by weight of the molding composition.
 21. The moldingcomposition of claim 19, further comprising a phenolic novolac hardener.22. The molding composition of claim 21, wherein the amount of thephenolic novolac hardener ranges from about 1.5 wt. % to about 10 wt. %based on the total weight of the molding composition.
 23. The moldingcomposition of claim 19, wherein the molding composition comprises anepoxy cresol novolac resin.
 24. The molding composition of claim 19,wherein the molding composition further comprises a biphenyl epoxyresin.
 25. The molding composition of claim 19, wherein the amount ofthe epoxy resin ranges from about 4 wt. % to about 12 wt. % based on thetotal weight of the molding composition.
 26. A flame-retardant moldingcomposition substantially free of elemental halogen, phosphorous, andantimony, consisting essentially of: about 4 wt. % to about 12 wt. % ofan epoxy resin comprising an epoxy cresol novolac resin or a biphenylepoxy resin; about 0.1 wt. % to about 3.5 wt. % of melamine cyanurate;about 0.1 wt. % to about 2 wt. % of zinc borate; about 0.01 wt. % toabout 1 wt. % of a compound selected from one or more of zinc oxide or ametal polyhydroxide comprising one or both of aluminum trihydrate andmagnesium hydroxide; about 0.001 wt. % to about 10 wt. % of a phenolicnovolac hardener; about 0 wt. % to about 90 wt. % of one or moresolvents; and about 0.1 wt. % to about 10 wt. % each of one or moreadditives selected from the group consisting of colorants, mold releaseagents, coupling agents, catalysts, ion scavengers, metal oxides, metalhydroxides, pigments, adhesion promoters, toughening agents, UVabsorbers, and antioxidants.
 27. The molding composition of claim 26,wherein the epoxy resin comprises an epoxy cresol novolac resin.
 28. Themolding composition of claim 26, wherein the epoxy resin comprises abiphenyl epoxy resin.
 29. A method of coating an electrical orelectronic device, comprising heating a molding composition to atemperature sufficient to cure the molding composition and form apolymer on the surface of the device; wherein the molding composition,which is substantially free of elemental halogen, phosphorus, andantimony, comprises: an epoxy resin; from about 0.1 to about 4 percentby weight of the molding composition of melamine cyanurate; from about0.1 to about 2 percent by weight of one or more metal borate salts; andfrom about 0.01 to about 1 percent by weight of a compound selected fromzinc oxide or one or more polyhydroxides of one or more elementsselected from Group IIA elements and Group IIIB elements.
 30. The methodof claim 29, wherein the temperature ranges from about 165° C. to about195° C.
 31. The method of claim 29, wherein the melamine cyanurate ispresent in the molding composition at from about 0.1 to about 3.5percent by weight of the molding composition; the metal borate salt ispresent at from about 0.2 to about 1.75 percent by weight of the moldingcomposition; and the compound selected from zinc oxide or one or morepolyhydroxides is present at from about 0.01 to about 0.85 percent byweight of the molding composition.
 32. The method of claim 29, whereinthe metal borate salt comprises zinc borate and the polyhydroxide is ametal polyhydroxide comprising one or both of aluminum trihydrate ormagnesium hydroxide.
 33. The method of claim 29, wherein the moldingcomposition further comprises a phenolic novolac hardener.
 34. Themethod of claim 33, wherein the amount of the phenolic novolac hardenerranges from about 1.5 wt. % to about 10 wt. % based on the total weightof the molding composition.
 35. The method of claim 29, wherein themolding composition contains an epoxy cresol novolac resin.
 36. Themethod of claim 29, wherein the molding composition further contains abiphenyl epoxy resin.
 37. The method of claim 29, wherein the amount ofthe epoxy resin in the molding composition ranges from about 4 wt. % toabout 12 wt. % based on the total weight of the molding composition. 38.The method of claim 37, wherein the amount of the epoxy resin in themolding composition ranges from about 5.5 wt. % to about 8.5 wt. % basedon the total weight of the molding composition.
 39. The method of claim29, wherein the device is an electrical or electronic device.
 40. Themethod of claim 39, wherein the electrical or electronic device isselected from a semiconductor, a transistor, a diode, or an integratedcircuit.
 41. An electrical or electronic device formed by the method ofclaim 29.